Seismic investigations over the 15 last years in marine basins around the world have revealed the common occurrence of sets of extensional faults that intersect to form networks of large polygons, each hundreds of meters to more than a kilometer across. Although polygonal faults been studied remotely in over 100 basins worldwide, extensive on-land exposures that lend themselves to field study have remained elusive. The article reports on the author's discovery of a polygonal fault system in chalk near Farafra Oasis, Egypt. A unique combination of regional structure, topography, and a hyperarid climate has resulted in almost continuous exposure of polygonal faults over an area of nearly 1000 km.

“We first discovered the faults in high resolution satellite imagery in Google Earth, where their polygonal pattern is spectacularly revealed. Our subsequent field work established that they are, in fact, the same type of polygonal faults that have been documented by the oil industry beneath modern oceans using seismic studies. Because we have actual field exposures at Farafra, we have been able to study the small-scale features of polygonal faults that are difficult, if not impossible, to study remotely using seismic data. Given how common polygonal faults are in modern marine basins, they should actually be quite common in the geologic record. Our field observations, which provide new insights into polygonal fault systems, should help geologists recognize incomplete or poorly exposed field occurrences elsewhere on land.”

Tewksbury is the lead principal investigator on a National Science Foundation grant that has partially funded this work. Over the past five years, she has initiated collaborations with researchers at five Egyptian universities and three U.S. universities. In December and January 2011, Tewksbury also led field work in the Western Desert of Egypt in which Claire Sayler ‘12, Peter Laciano ‘13 and Tucker Keren ‘13 participated.